JP5880327B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control device that introduces purge gas containing evaporated fuel from a fuel tank into an intake system.

  2. Description of the Related Art Conventionally, there is known a technique for preventing leakage of fuel components to the outside of a vehicle by guiding fuel gas volatilized in a fuel tank of a vehicle into an engine cylinder. That is, the fuel gas in the fuel tank is temporarily recovered by the canister, and the fuel gas (purge gas) desorbed from the canister is introduced into the intake passage. A purge control valve for adjusting the flow rate of the purge gas is interposed on the purge passage connecting the canister and the intake passage, and the opening degree is controlled according to the operating state of the engine.

  The air-fuel ratio of the air-fuel mixture introduced into the cylinder of the engine changes according to the purge gas concentration. Therefore, a technique for appropriately controlling the air-fuel ratio by accurately estimating the purge gas concentration has been developed. For example, a technique is known in which an air-fuel ratio sensor is provided on an exhaust passage to detect an air-fuel ratio, and a purge gas concentration is estimated based on a difference between the detected air-fuel ratio and a target air-fuel ratio. There is also a technique for calculating an air-fuel ratio feedback correction coefficient corresponding to the ratio between the air-fuel ratio and the target air-fuel ratio and learning the purge gas concentration based on the change in the correction coefficient (see, for example, Patent Documents 1 and 2). ).

JP-A-7-63078 JP-A-8-284713

  However, the purge gas concentration calculation method based on the air-fuel ratio detected by the air-fuel ratio sensor has a problem that the calculation error of the concentration estimated value due to the air-fuel ratio detection error tends to increase. In particular, when the air-fuel ratio is larger than the target air-fuel ratio (lean), the controllability of the air-fuel ratio is likely to deteriorate due to the calculation error of the concentration estimation value.

  For example, if the purge control valve is opened while the fuel gas is not adsorbed to the canister, air that does not contain a fuel component is introduced into the intake system, and is emptied according to the amount of air introduced from the purge passage side. The fuel ratio increases. If the amount of air introduced from the purge passage side is 10% compared to the amount of air sucked from the throttle valve side, the rate of increase of the air-fuel ratio is expected to be 10% if the fuel injection amount is constant. Is done.

  At this time, if an increase in air-fuel ratio exceeding 10% is detected due to detection error of the air-fuel ratio sensor, the calculated concentration of air introduced from the purge passage side becomes a negative value. Even if the detection value of the air-fuel ratio sensor is accurate, the same result can be produced when the amount of air sucked from the throttle valve side is large or when the fuel injection amount is small. On the other hand, the minimum value of the fuel concentration is 0, and since the fuel concentration is an equivalent ratio, it does not become a negative value. Thus, if an incorrect numerical value is calculated in the process of calculating the concentration estimation value, the air / fuel ratio of the engine cannot be controlled appropriately.

One of the objects of the present case has been devised in view of the above-described problems, and is to provide an engine control apparatus that improves the estimation accuracy of the purge gas concentration.
It should be noted that the present invention is not limited to these purposes, and is an operational effect derived from each configuration shown in the embodiment for carrying out the invention described later, and also has an operational effect that cannot be obtained by conventional techniques. Can be positioned as

(1) An engine control device disclosed herein is a purge rate calculation for calculating a purge rate corresponding to the purge gas introduction ratio in an engine control device for introducing purge gas containing evaporated fuel from a fuel tank into an intake system. And a correction coefficient calculating means for calculating a fuel amount correction coefficient for setting the actual air-fuel ratio of the engine to the target air-fuel ratio.
A purge concentration calculating means for calculating a concentration of the purge gas based on the fuel amount correction coefficient calculated by the correction coefficient calculating means and the purge rate calculated by the purge rate calculating means; and the purge rate calculating Limiting means for setting an upper limit value of the fuel amount correction coefficient calculated by the correction coefficient calculation means based on the purge rate calculated by the means. The limiting means lowers the upper limit value as the purge rate is lower.

  The purge gas introduction ratio is, for example, the ratio of the purge gas amount to the intake air amount introduced through the throttle valve of the engine, or the ratio of the purge gas amount to the total intake air amount introduced into the cylinder of the engine. is there.

Incidentally, the restriction means, if example embodiment, a value obtained by adding 1 to the purge rate expressed in percentage, it is preferable to set the upper limit.

( 2 ) It is preferable that air-fuel ratio calculating means for calculating the actual air-fuel ratio based on detection information of a sensor provided in the exhaust system of the engine is preferably provided.
In this case, it is preferable that the purge rate calculation means calculates, as the purge rate, a sensor portion purge rate that is an introduction rate considering a delay time until the purge gas introduced into the intake system reaches the sensor. . Further, it is preferable that the limiting means sets an upper limit value of the fuel amount correction coefficient based on the sensor portion purge rate.

  It is preferable to provide a target setting means for setting a target air-fuel ratio of the intake air of the engine. In this case, the correction coefficient calculating means calculates the fuel amount correction coefficient based on a ratio between the target air-fuel ratio set by the target setting means and the actual air-fuel ratio calculated by the air-fuel ratio calculating means. It is preferable to calculate.

( 3 ) In addition, air amount calculating means for calculating the amount of air introduced into the cylinder of the engine is provided, and the purge rate calculating means is based on the air amount calculated by the air amount calculating means. It is preferable to estimate the time.
The delay time is preferably estimated in consideration of an intake delay, combustion delay, and exhaust delay of air introduced into the cylinder of the engine. The “air amount” referred to here includes the volume and mass of air introduced (introduced) into the cylinder of the engine, or parameters corresponding thereto, and includes, for example, charging efficiency and volume efficiency.

( 4 ) Moreover, it is preferable that the said limitation means changes the said upper limit according to the code | symbol or magnitude | size of the change gradient of the said purge rate.
For example, when the change gradient is negative, it is conceivable to set the upper limit value smaller than when the change gradient is positive. Further, the behavior of the upper limit value may be predicted based on the change rate of the purge rate, focusing on the characteristic that the change rate of the purge rate corresponds to the change rate of the upper limit value. In this case, it is conceivable to set the upper limit value so that the value of the fuel amount correction coefficient that is limited in the current calculation cycle does not exceed the upper limit value in the next calculation cycle.

  According to the disclosed engine control device, the upper limit value of the fuel amount correction coefficient is set based on the purge rate, thereby reducing the calculation error of the fuel amount correction coefficient. In particular, it is possible to prevent an erroneous calculation such that the purge gas concentration is estimated as a negative value, and to improve the calculation accuracy of the purge gas concentration. Thereby, the engine can be controlled using the purge gas concentration with high estimation accuracy, and the controllability of the air-fuel ratio can be improved.

It is a figure which illustrates the block configuration of the control apparatus of the engine which concerns on one Embodiment, and the structure of the engine to which this control apparatus was applied. It is a graph for demonstrating the exhaust response delay of the engine to which this control apparatus was applied. (A), (b) is a graph which illustrates the relationship between the purge gas concentration estimated by this control apparatus, and a purge rate. It is a flowchart which illustrates the estimation procedure of the purge gas density | concentration in this control apparatus. It is a graph for demonstrating the upper limit of the fuel quantity correction coefficient calculated with this control apparatus, (a), (c) is a time-dependent fluctuation | variation of a purge rate, (b), (d), (e) is a fuel. The variation with time of the amount correction coefficient is shown.

  An engine control apparatus will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment. Each configuration of the present embodiment can be implemented with various modifications without departing from the spirit of the present embodiment, and can be selected or combined as necessary.

[1. Device configuration]
[1-1. engine]
The engine control device of the present embodiment is applied to the in-vehicle gasoline engine 10 shown in FIG. Here, one of a plurality of cylinders provided in the multi-cylinder engine 10 is shown. The piston 16 is provided so as to be slidable back and forth along the inner peripheral surface of a cylinder 19 formed in a hollow cylindrical shape. The space surrounded by the upper surface of the piston 16 and the inner peripheral surface and top surface of the cylinder 19 functions as a combustion chamber 26 of the engine.

  The lower portion of the piston 16 is connected to a crank arm having a central axis that is eccentric from the axis of the crankshaft 17 via a connecting rod. Thereby, the reciprocating motion of the piston 16 is transmitted to the crank arm and converted into the rotational motion of the crankshaft 17.

  An intake port 11 for supplying intake air into the combustion chamber 26 and an exhaust port 12 for discharging exhaust gas after combustion in the combustion chamber 26 are formed in the top surface of the cylinder 19. Further, in each of the intake port 11 and the exhaust port 12, an intake valve 14 and an exhaust valve 15 are provided at an end portion on the combustion chamber 26 side. The intake valve 14 and the exhaust valve 15 are individually controlled in operation by a valve mechanism (not shown) provided in the upper part of the engine 10.

A spark plug 13 is provided at the top of the cylinder 19 with its tip projecting toward the combustion chamber 26. The ignition timing by the spark plug 13 is controlled by the engine control device 1 described later.
A water jacket 27 is provided around the cylinder 19 to circulate engine cooling water therein. The engine cooling water is a refrigerant for cooling the engine 10 and circulates in the cooling water circulation path that connects the water jacket 27 and the radiator in an annular shape.

[1-2. Intake and exhaust system]
An injector 18 for injecting fuel is provided in the intake port 11. The amount of fuel injected from the injector 18 is controlled by the engine control device 1 described later. Further, an intake manifold 20 (hereinafter referred to as an intake manifold) is provided upstream of the injector 18 in the intake air flow. The intake manifold 20 is provided with a surge tank 21 for temporarily storing air flowing toward the intake port 11 side. The intake manifold 20 on the downstream side of the surge tank 21 is formed to branch toward the intake ports 11 of the plurality of cylinders 19, and the surge tank 21 is located at the branch point. The surge tank 21 functions to alleviate intake pulsation and intake interference that can occur in each cylinder.

  A throttle body 22 is connected to the upstream side of the intake manifold 20. An electronically controlled throttle valve 23 is built in the throttle body 22, and the amount of air flowing to the intake manifold 20 is adjusted according to the opening (throttle opening) of the throttle valve 23. The throttle opening is controlled by the engine control device 1.

  An intake passage 24 is connected further upstream of the throttle body 22, and an air filter is interposed further upstream of the intake passage 24. Thus, fresh air filtered by the air filter is supplied to each cylinder 19 of the engine 10 via the intake passage 24 and the intake manifold 20.

  The surge tank 21 is connected to a purge passage 30 for introducing the fuel gas desorbed from the canister 29 into the intake system. An electromagnetic purge valve 31 that controls the flow rate of the fuel gas purged from the canister 29 (purge gas) into the surge tank 21 is interposed on the purge passage 30. The opening degree of the purge valve 31 is controlled by the engine control device 1.

  Activated carbon 29 a is built in the canister 29. The fuel gas containing the evaporated fuel generated in the fuel tank 28 is adsorbed and recovered by the activated carbon 29a. The canister 29 is connected to a passage 29b for sucking outside fresh air. When the purge valve 31 is opened, fresh air is introduced into the canister 29 through the passage 29b, and the fuel gas desorbed from the activated carbon 29a is supplied to the surge tank 21 through the purge passage 30.

  An exhaust manifold 25 (hereinafter referred to as an exhaust manifold) is provided on the downstream side of the exhaust port 12. The exhaust manifold 25 is formed in a shape for joining the exhaust gases from the cylinders 19 and is connected to an exhaust passage, an exhaust catalyst device, or the like (not shown) on the downstream side thereof.

[1-3. Detection system]
An air-fuel ratio sensor 32 is provided at an arbitrary position downstream of the exhaust manifold 25 to grasp the air-fuel ratio AF (the air-fuel ratio of the air-fuel mixture before combustion) of the air-fuel mixture burned in the combustion chamber 26. . The air-fuel ratio sensor 32 is, for example, an oxygen concentration sensor or LAFS (linear air-fuel ratio sensor), and detects exhaust air-fuel ratio information corresponding to the concentration of oxygen component contained in the exhaust gas.

  An air flow sensor 33 that detects an intake air flow rate Q is provided in the intake passage 24. The intake flow rate Q is a parameter corresponding to the flow rate of air passing through the throttle valve 23. The intake air flow from the throttle valve 23 to the cylinder 19 has a so-called intake response delay (a delay until the air that has passed through the throttle valve 23 is introduced into the cylinder 19), and is thus introduced into the cylinder 19 at a certain time. The flow rate of air does not necessarily match the flow rate of air passing through the throttle valve 23 at that time. In addition, an intake response delay similar to the intake flow from the throttle valve 23 occurs in the purge gas flow that has passed through the purge valve 31.

  Further, an exhaust response delay occurs in the exhaust flow from the cylinder 19 to the attachment position of the air-fuel ratio sensor 32. Therefore, the exhaust air / fuel ratio information detected by the air / fuel ratio sensor 32 at a certain time corresponds to the air / fuel ratio of the fuel mixed with the air that has passed through the throttle valve 23 in the past (or the purge gas that has passed through the purge valve 31 in the past). Therefore, it does not necessarily correspond to the intake flow rate Q or the purge gas flow rate at that time. In the engine control apparatus 1, the purge gas concentration is calculated in consideration of such influences as intake response delay, exhaust response delay, and the like.

A cooling water temperature sensor 34 for detecting the temperature of the engine cooling water (cooling water temperature W _T ) is provided at an arbitrary position on the water jacket 27 or the cooling water circulation path. The crankshaft 17 is provided with an engine rotation speed sensor 35 that detects the rotation angle. The amount of change (angular velocity) of the rotation angle per unit time is proportional to the rotation speed Ne (actual rotation number per unit time) of the engine 10. Therefore, the engine rotation speed sensor 35 of the present embodiment has a function of acquiring the rotation speed Ne of the engine 10. Note that the rotational speed Ne may be calculated inside the engine control device 1 based on the rotational angle detected by the engine rotational speed sensor 35.

At an arbitrary position of the vehicle, an accelerator opening sensor 36 that detects an accelerator pedal depression amount (accelerator operation amount A _PS ) and a brake fluid pressure sensor 37 that detects a brake fluid pressure _BRK corresponding to the brake operation amount. And are provided. The accelerator operation amount A _PS is a parameter corresponding to the driver's acceleration request and intention to start, in other words, a parameter correlated to the load of the engine 10 (output request to the engine 10). Further, the brake fluid pressure B _RK during normal vehicle travel is a parameter corresponding to the driver's deceleration request and intention to stop.

The exhaust gas air-fuel ratio information, intake air flow rate Q, cooling water temperature W _T , rotational speed Ne, accelerator operation amount A _PS , and brake fluid pressure B _RK acquired by the various sensors 32 to 37 are sent to the engine control device 1. Communicated.

[1-4. Control system]
A vehicle equipped with the engine 10 is provided with an engine control device 1 (Engine Electronic Control Unit). The engine control apparatus 1 is configured as an LSI device or an embedded electronic device in which a microprocessor, ROM, RAM, and the like are integrated, and is connected to a communication line of an in-vehicle network network provided in the vehicle. Note that various known electronic control devices such as a brake control device, a transmission control device, a vehicle stability control device, an air conditioning control device, and an electrical component control device are communicably connected to each other on the in-vehicle network. An electronic control device other than the engine control device 1 is called an external control system, and a device controlled by the external control system is called an external load device.

  The engine control device 1 is an electronic control device that comprehensively controls a wide range of systems such as an ignition system, a fuel system, an intake / exhaust system, and a valve system related to the engine 10, and the amount of air supplied to each cylinder 19 of the engine 10. Further, the amount of purge gas, the amount of fuel injected from the injector 18, the ignition timing of each cylinder 19 and the like are controlled.

  The signal input side of the engine control device 1 is connected to the air-fuel ratio sensor 32, the air flow sensor 33, the coolant temperature sensor 34, the engine rotation speed sensor 35, the accelerator opening sensor 36, and the brake fluid pressure sensor 37 described above. On the other hand, the engine 10 is connected to the control signal output side, and the amount of air supplied to each cylinder 19 of the engine 10, the fuel injection amount, the ignition timing of each cylinder, and the like are controlled. Specific control objects of the engine control device 1 include the amount of fuel injected from the injector 18 and the injection timing, the ignition timing at the spark plug 13, the opening degree of the throttle valve 23 and the purge valve 31, and the like.

Note that the engine control device 1 outputs a control signal to these valves so that the target opening of the throttle valve 23 and the purge valve 31 is calculated and the actual opening of the valve matches the target opening. Combined with functions. The target opening degree of each valve calculated in the engine control device 1 corresponds to the actual opening degrees S ₁ and S ₂ of the respective valves. Therefore, it can be said that the engine control apparatus 1 has a function of acquiring the respective opening degrees S ₁ and S ₂ of the throttle valve 23 and the purge valve 31 that are controlled objects.

[2. Control configuration]
The air-fuel ratio control performed by the engine control device 1 will be described. Air-fuel ratio of the mixture introduced into the cylinder 19, the opening degree S ₁ of the throttle valve 23, the opening degree S ₂ of the purge valve 31 is determined by the fuel injection amount and the purge gas concentration from the injector 18. Among these parameters, the opening degrees S ₁ and S ₂ and the fuel injection amount are objects to be controlled by the engine control device 1 and can be changed by the engine control device 1 independently.

On the other hand, the purge gas concentration is a parameter that varies depending on the fuel evaporation rate and elapsed time from the fuel tank 28, the pressure in the canister 29, the temperature, the performance of the activated carbon 29a, and the like. Can not. Therefore, the engine control device 1 appropriately controls the air-fuel ratio of the engine 10 by changing the opening degrees S ₁ and S ₂ and the fuel injection amount while estimating the purge gas concentration value as needed.

  The fuel injection amount in the injector 18 is controlled mainly by two methods of feedback injection control and open loop injection control. The feedback injection control is feedback control in which the result of fuel injection is reflected in the setting of the target fuel injection amount that is the cause. In the feedback injection control, the fuel injection amount from the injector 18 is adjusted based on the exhaust air / fuel ratio information detected by the air / fuel ratio sensor 32. In addition, when the target value of the air-fuel ratio by the food back injection control is the stoichiometric air-fuel ratio (stoichiometric), it is also called stoichiometric feedback injection control.

On the other hand, the open loop injection control is control for adjusting the fuel injection amount without using the exhaust air / fuel ratio information detected by the air / fuel ratio sensor 32. The open loop injection control is performed, for example, when any of the operation states listed below is applicable. On the other hand, when none of the operating states is applicable, feedback injection control is performed.
A. Elapsed time after the engine 10 is started is within a predetermined time B. C. The air-fuel ratio sensor 32 itself is in a cold state. The coolant temperature W _T of the engine 10 is below the warm-up temperature.

  As shown in FIG. 1, the engine control apparatus 1 includes a charging efficiency calculation unit 2, a target air-fuel ratio setting unit 3, an air-fuel ratio calculation unit 4, a purge rate calculation unit 5, a fuel amount correction coefficient calculation unit 6, and an upper limit value limit. A unit 7, a purge concentration calculation unit 8 and a control unit 9 are provided. Each of these elements may be realized by an electronic circuit (hardware), may be programmed as software, or some of these functions may be provided as hardware, and the other part as software. It may be what you did.

  The charging efficiency calculation unit 2 (air amount calculation means) calculates the charging efficiency Ec based on the intake flow rate Q detected by the air flow sensor 33. The charging efficiency Ec is a parameter corresponding to the amount of air actually introduced into the cylinder 19, and the volume of air charged into the cylinder 19 during one intake stroke is a standard state (0 ° C., 1 Normalized to the gas volume at atmospheric pressure) and then divided by the cylinder volume. Here, for the cylinder 19 to be controlled, the amount of air actually sucked into the cylinder 19 is calculated from the sum of the intake flow rate Q detected by the airflow sensor 33 during the previous intake stroke. Efficiency Ec is calculated. The charging efficiency Ec calculated here is transmitted to the purge rate calculation unit 5.

  Strictly speaking, the charging efficiency Ec obtained based on the intake flow rate Q corresponds to the amount of air sucked into the cylinder 19 after the calculation time. Therefore, for the exhaust gas whose sensor air-fuel ratio AF has been detected by the air-fuel ratio sensor 32, in order to obtain the air amount when the exhaust gas is introduced into the cylinder 19, a point in time earlier than the detection time by the air-fuel ratio sensor 32 is obtained. The charging efficiency Ec may be calculated based on the intake flow rate Q at. Alternatively, after obtaining the air amount based on the latest intake flow rate Q, it is considered that a delay calculation simulating a predetermined intake response delay or exhaust response delay is performed to reach the vicinity of the air-fuel ratio sensor 32. What is necessary is just to obtain | require the filling efficiency Ec about exhaust_gas | exhaustion.

The target air-fuel ratio setting unit 3 (target setting means) sets the target air-fuel ratio AF _TGT according to the load required for the engine 10. The load referred to here includes, for example, a driver-requested load that is set according to the accelerator pedal depression amount, an external load that is set according to the operating state of the external load device, and the like. The target air-fuel ratio AF _TGT may be set in any of the above-described feedback injection control and open loop injection control, or may be set only during feedback injection control. Information on the target air-fuel ratio AF _TGT set here is transmitted to the fuel amount correction coefficient calculation unit 6, the purge concentration calculation unit 8, and the control unit 9.

The air-fuel ratio calculation unit 4 (air-fuel ratio calculation means) calculates the air-fuel ratio of the air-fuel mixture actually introduced into the cylinder 19. Here, the air-fuel ratio AF (actual air-fuel ratio) is calculated based on the exhaust air-fuel ratio information detected by the air-fuel ratio sensor 32. The information of the air-fuel ratio AF calculated here is transmitted to the fuel amount correction coefficient calculation unit 6, the purge concentration calculation unit 8 and the control unit 9. Hereinafter, this air-fuel ratio AF is referred to as sensor air-fuel ratio AF. Further, the air-fuel ratio of the purge gas is referred to as a purge gas air-fuel ratio AF _{PRG in} distinction from the sensor air-fuel ratio AF.

The purge rate calculation unit 5 (purge rate calculation means) calculates a purge rate R _PRG and a sensor unit purge rate R _PRGS corresponding to the purge gas introduction rate. Here, the “introduction ratio” means the ratio of the purge gas amount to the entire intake air amount or the ratio of the purge gas amount to the intake air flowed from the throttle valve 23 side. In the purge rate calculation unit 5 of the present embodiment, the latter is calculated as the purge rate R _PRG .

The flow rate of the intake air passing through the throttle valve 23 is calculated from the flow rate of the intake air and the opening S _{1 of the} throttle valve 23. The flow velocity is calculated based on the intake flow rate Q, the pressures upstream and downstream of the throttle valve 23, the intake air temperature, and the like. Similarly, the purge gas flow rate is calculated from the opening S ₂ of the purge valve 31 and the purge gas flow rate, and the purge gas flow rate is calculated based on the pressure upstream and downstream of the purge valve 31, the loss pressure in the canister 29, the intake air temperature, and the like. Is done. A correction coefficient having a magnitude corresponding to the pressure difference of the throttle valve 23 and the pressure ratio (for example, the ratio of the downstream pressure to the upstream pressure) is set, and the opening of the purge valve 31 relative to the opening S ₁ of the throttle valve 23 are multiplied by the correction coefficient on the ratio of S ₂ may be determined as a purge rate R _PRG.

The purge rate R _PRG corresponds to the introduction ratio when the purge gas is introduced from the purge passage 30 into the surge tank 21 of the intake system. On the other hand, the purge rate calculation unit 5 is the ratio of the gas introduced as purge gas into the cylinder 19 and the gas introduced as fresh air from the throttle valve 23 side in the exhaust gas that has reached the vicinity of the air-fuel ratio sensor 32. The sensor part purge rate R _PRGS corresponding to is calculated. This sensor portion purge rate R _PRGS corresponds to the past purge rate R _PRG and is determined in consideration of the delay time until the purge gas introduced into the intake system reaches the vicinity of the air-fuel ratio sensor 32.

The delay time until the purge gas reaches the sensor is estimated based on the charging efficiency Ec calculated by the charging efficiency calculation unit 2. For example, by applying a first-order lag processing and second delay processing on the purge rate R _PRG, generates a variation trajectory of the actual exhaust response delay purge rate R _PRG simulating the which the sensor unit purge rate R _PRGS It is possible to do. As a simple method, the difference between the sensor unit purge rate R _PRGS obtained in the previous calculation cycle and the purge rate R _PRG obtained in the current calculation cycle is multiplied by a predetermined filter coefficient. It can be considered that this is added to the input value of the cycle, and this is used as the sensor portion purge rate R _PRGS of the current calculation cycle.

In any method, the purge rate calculation unit 5 is configured such that the higher the filling efficiency Ec, the shorter the delay time of the sensor portion purge rate R _PRGS with respect to the purge rate R _PRG (the lower the filling efficiency Ec, the longer the delay time). Give the time constant and filter coefficient to be longer). The value of the sensor portion purge rate R _PRGS calculated here is transmitted to the upper limit value limiting portion 7, the purge concentration calculating portion 8 and the control portion 9.

  FIG. 2 illustrates the relationship between the delay time until the purge gas that has passed through the purge valve 31 affects the air-fuel ratio sensor 32 and the charging efficiency Ec. This delay time corresponds to a time obtained by combining the intake response delay time of the purge gas and the exhaust response delay time. The intake response delay time is a delay time until the purge gas that has passed through the purge valve 31 is introduced into the cylinder 19. For example, a time lag from when the purge valve 31 is opened to the start of the intake stroke, and intake resistance This includes the delay time due to intake inertia. The exhaust response delay time is a delay time until the exhaust after combustion reaches the vicinity of the air-fuel ratio sensor 32 after the purge gas is introduced into the cylinder 19, for example, a combustion cycle from the intake stroke to the exhaust stroke. This includes the delay time required for exhaust gas and the delay time due to the effects of exhaust resistance and exhaust inertia.

Here, a fuel injection amount from the intake air amount and the injector 18 to pass through the throttle valve 23 is constant, the air-fuel ratio when the purge valve 31 is closed and a AF _1. Further, it is assumed that purge gas richer than the air-fuel ratio AF ₁ exists in the purge passage 30 and that the theoretical value of the air-fuel ratio changes from AF ₁ to AF ₂ by opening the purge valve 31.

  When the purge valve 31 is opened at time 0, the theoretical value of the air-fuel ratio changes stepwise as shown by a thick solid line in FIG. On the other hand, the purge gas that has passed through the purge valve 31 is not immediately introduced into the cylinder 19, but in the vicinity of the air-fuel ratio sensor 32 with an intake response delay and an exhaust response delay as shown by a thin solid line in FIG. To reach. Therefore, the sensor air-fuel ratio AF gradually changes with a delay from time 0.

The purge gas delay time is introduced into the cylinder 19 for each combustion cycle and changes according to the amount of air discharged, that is, the charging efficiency Ec. Each change of the sensor air-fuel ratio AF when the value of the charging efficiency Ec is Ec ₁ , Ec ₂ , Ec ₃ (Ec ₃ <Ec ₂ <Ec ₁ ) is shown by a thin solid line, a broken line, and a one-dot chain line in FIG. Show. The higher the charging efficiency Ec, the faster the purge gas reaches the air-fuel ratio sensor 32, and the delay time is shortened. On the contrary, the lower the charging efficiency Ec, the longer the delay time becomes, and the sensor air-fuel ratio AF becomes difficult to change.

The fuel amount correction coefficient calculation unit 6 (correction coefficient calculation means) calculates a fuel amount correction coefficient K _{FB_PRG} mainly used in feedback injection control. The fuel amount correction coefficient K _{FB_PRG} is a parameter indicating how much the sensor air-fuel ratio AF has deviated from the target air-fuel ratio AF _TGT. The sensor air-fuel ratio AF (actual air-fuel ratio) of the engine 10 is set to the target air-fuel ratio AF. _This is a correction coefficient to match _TGT .

Here, first, the fuel amount correction coefficient K _{FB_PRG} is calculated based on the target air-fuel ratio AF _TGT and the sensor air-fuel ratio AF, and then a value limited by an upper limit value K _MAX calculated by an upper limit value limiter 7 described later. Is calculated as the final fuel amount correction coefficient K _{FB_PRG} . Therefore, the fuel amount correction coefficient K _{FB_PRG} is _smaller between the theoretical value obtained based on the target air-fuel ratio AF _TGT and the sensor air-fuel ratio AF and the upper limit value K _MAX limited by the upper limit value limiting unit 7. One value is assumed. The value of the fuel amount correction coefficient K _{FB_PRG} calculated here is transmitted to the purge concentration calculation unit 8 and the control unit 9.

The fuel amount correction coefficient K _{FB_PRG} is a parameter corresponding to the reciprocal of the fuel concentration of the exhaust gas that has been detected by the air-fuel ratio sensor 32. In other words, the fuel amount correction coefficient K _{FB_PRG} is a parameter for feeding _back the sensor air-fuel ratio AF information to future control, and is a coefficient that gives an increase / decrease amount for bringing the sensor air-fuel ratio AF closer to the target air-fuel ratio AF _TGT. It becomes.
The fuel amount correction coefficient K _{FB - PRG} is, K _{FB - PRG} <1.0 next when the sensor air-fuel ratio AF is K _{FB - PRG} = 1.0, and the sensor air-fuel ratio AF is richer than the target air-fuel ratio AF _TGT when equal to the target air-fuel ratio AF _TGT When the air-fuel ratio is leaner than the target air-fuel ratio AF _TGT , K _{FB_PRG} > 1.0. When the target air-fuel ratio AF _TGT is the stoichiometric air-fuel ratio, the fuel amount correction coefficient K _{FB_PRG} is a parameter corresponding to the excess air ratio.

Note that the deviation amount between the sensor air-fuel ratio AF and the target air-fuel ratio AF _TGT includes the deviation amount due to the purge gas (purge gas concentration calculation error, purge gas flow rate calculation error, etc.) and the deviation amount due to factors other than the purge gas (from the injector 18). Injection error, adhesion to intake manifold 20, detection error in air-fuel ratio sensor 32, and the like. Therefore, the purge concentration correction coefficient K ₁ for making the former deviation amount zero and the air-fuel ratio feedback correction coefficient K ₂ for making the latter deviation amount zero are separately calculated and multiplied by the fuel. The amount correction coefficient K _{FB_PRG} may be obtained.

In this case, the purge concentration correction coefficient K ₁ is calculated based on, for example, the opening degree S ₂ of the purge valve 31, the purge rate R _PRG , the previous value of the purge gas concentration estimated value K _{AF_PRG} described later, and the like. Further, the air-fuel ratio feedback correction coefficient K _2, for example the opening S ₁ of the intake flow rate Q and the throttle valve 23, the upstream and downstream pressure of the throttle valve 23, the intake air temperature is calculated based on the sensor an air-fuel ratio AF and the like.

The upper limit limiting unit 7 (limiting unit) _sets the upper limit value K _MAX of the fuel amount correction coefficient K _{FB_PRG} calculated by the fuel amount correction coefficient calculating unit 6 based on the purge rate R _PRG calculated by the purge rate calculating unit 5. It is set to limit the calculated value of the fuel amount correction coefficient K _{FB_PRG} . Here, the upper limit value K _MAX is calculated based on the sensor portion purge rate R _PRGS that takes into account the delay time until the purge gas introduced into the intake system reaches the vicinity of the air-fuel ratio sensor 32.

Further, the upper limit limiting unit 7 sets an upper limit K _MAX having a different calculation method according to the sign of the change gradient of the sensor unit purge rate R _PRGS . Here, when the sensor portion purge rate R _PRGS is increasing (the change gradient is positive), a value obtained by adding the predetermined value A to the sensor portion purge rate R _PRGS is set as the upper limit value K _MAX . On the other hand, when the sensor purge rate R _PRGS is decreasing (change gradient is negative) or constant (change gradient is 0), a second predetermined value B smaller than the predetermined value A is set to the sensor purge rate R _PRGS . The added value is set as the upper limit value K _MAX .

Thus, (loose limit) upper limit K _MAX is high in the process of the sensor unit purge rate R _PRGS increases is set, strict upper limit K _MAX is low (limited in the process of the sensor unit purge rate R _PRGS is lowered in the opposite ) Is set. Further, when the sensor portion purge rate R _PRGS is constant, the upper limit value K _MAX is set slightly lower than when the value is increasing, thereby increasing the limit. The upper limit value K _MAX calculated here is transmitted to the fuel amount correction coefficient calculation unit 6. The specific values of the predetermined value A and the second predetermined value B are arbitrary, but are set so that at least the inequality 1 ≦ A ≦ B is satisfied, for example, A = 1.00, B = 0.97 .

The purge concentration calculation unit 8 (purge concentration calculation means) includes a fuel amount correction coefficient K _{FB_PRG} calculated by the fuel amount correction coefficient calculation unit 6 and a purge rate R _PRG (or sensor unit purge rate calculated by the purge rate calculation unit 5). R _PRGS ), a purge gas concentration estimated value K _{AF_PRG} corresponding to the estimated purge gas concentration is calculated. The definition of the purge gas concentration estimated value K _{AF_PRG} is _{obtained by dividing} the target air-fuel ratio AF _TGT by the purge gas air-fuel ratio AF _PRG .

The purge gas concentration estimated value K _{AF_PRG} has a value corresponding to the fuel concentration of the purge gas contained in the exhaust gas whose sensor air-fuel ratio AF is detected by the air-fuel ratio sensor 32. For example, when the purge gas air-fuel ratio AF _PRG is equal to the target air-fuel ratio AF _TGT , K _{AF_PRG} = 1.0, and when the purge gas air-fuel ratio AF _PRG is richer than the target air-fuel ratio AF _TGT , K _{AF_PRG} > 1.0 and the purge gas air-fuel ratio AF _{When PRG} is leaner than the target air-fuel ratio AF _TGT , K _{AF_PRG} <1.0. When the target air-fuel ratio AF _TGT is the stoichiometric air-fuel ratio, the purge gas concentration estimated value K _{AF_PRG} is a parameter corresponding to the purge gas equivalent ratio.

The purge gas air-fuel ratio AF _PRG can be calculated based on the sensor air-fuel ratio AF, the purge rate R _PRG and the target air-fuel ratio AF _TGT . Alternatively, it can be calculated based on the fuel amount correction coefficient K _{FB_PRG} , the purge rate R _PRG and the target air-fuel ratio AF _TGT . Therefore, the purge gas concentration estimated value K _{AF_PRG} is _calculated as shown in Equations 1 to 3, such as sensor air-fuel ratio AF, fuel amount correction coefficient K _{FB_PRG} , purge rate R _PRG , sensor part purge rate R _PRGS , target air-fuel ratio AF _TGT, etc. It can be expressed by the function of

The purge concentration calculation unit 8 of the present embodiment calculates the purge gas concentration estimated value K _{AF_PRG} based on the fuel amount correction coefficient K _{FB_PRG} , the sensor unit purge rate R _PRGS and the target air-fuel ratio AF _TGT as shown in Equation 2. . Information of the purge gas concentration estimated value K _{AF_PRG} calculated here is transmitted to the control unit 9.

FIG. 3A is a graph _showing the relationship between the fuel amount correction coefficient K _{FB_PRG} , the purge rate R _PRG and the purge gas concentration estimated value K _{AF_PRG} . When the fuel amount correction coefficient K _{FB_PRG} is 1.0, the purge gas concentration estimated value K _{AF_PRG} is 1.0 regardless of the magnitude of the purge rate R _PRG . On the other hand, when the fuel amount correction coefficient K _{FB_PRG} is smaller than 1.0 (that is, when the exhaust gas is rich), the purge gas is approximately inversely proportional to the purge rate R _PRG as the value of the purge rate R _PRG decreases. The value of the density estimated value K _{AF_PRG} increases. If the fuel amount correction coefficient K _{FB_PRG} is smaller than 1.0 and the purge rate R _PRG is constant, the purge gas concentration estimated value K _{AF_PRG} increases as the value of the fuel amount correction coefficient K _{FB_PRG} decreases. The slope of the graph is steep.

Similarly, when the fuel amount correction coefficient K _{FB_PRG} is larger than 1.0 (that is, when the exhaust gas is lean), as the value of the purge rate R _PRG decreases, it is almost inversely proportional to the purge rate R _PRG. The purge gas concentration estimated value K _{AF_PRG} decreases. Further, if the fuel amount correction coefficient K _{FB_PRG} is larger than 1.0 and the purge rate R _PRG is constant, the purge gas concentration estimated value K _{AF_PRG} decreases as the value of the fuel amount correction coefficient K _{FB_PRG} increases. The slope of the graph is steep.

In the function shown in Equation 2 above, the purge gas concentration estimated value K _{AF_PRG} may be negative depending on the combination of the purge rate R _PRG and the fuel amount correction coefficient K _{FB_PRG} . Similarly, in the function shown in Expression 3, the purge gas concentration estimated value K _{AF_PRG} may be negative depending on the combination of the sensor portion purge rate R _PRGS and the fuel amount correction coefficient K _{FB_PRG} .

When the value of the purge gas concentration estimated value K _{AF - PRG} extracting a purge rate R _PRG and combinations of the fuel amount correction coefficient K _{FB - PRG} as a 0, the lower the purge rate R _PRG, fuel quantity correction corresponding to the purge rate R _PRG It has a characteristic that the value of the coefficient K _{FB_PRG} decreases. For the combination of the purge rate R _PRG and the fuel amount correction coefficient K _{FB_PRG where} the estimated purge gas concentration value K _{AF_PRG} is 0, the relationship shown in the following equation 4 is established.

For example, as shown in FIG. _3B , when the value of the fuel amount correction coefficient K _{FB_PRG} is 1.04, the purge gas concentration estimated value K in the graph showing the relationship between the purge gas concentration estimated value K _{AF_PRG} and the purge rate R _{PRG. The} purge rate R _PRG with the _{AF_PRG} value of 0 is 0.04. Similarly, when the value of the fuel amount correction coefficient K _{FB_PRG} is 1.05, the purge gas concentration estimated value K _{AF_PRG} is 0 when the purge rate R _PRG is 0.05, and the value of the fuel amount correction coefficient K _{FB_PRG} is 1.06 The purge gas concentration estimated value K _{AF_PRG} becomes 0 when the purge rate R _PRG is 0.06.

On the other hand, in the upper limit limiting unit 7, the upper limit K _{MAX of the} fuel amount correction coefficient K _{FB_PRG} is set by adding the predetermined value A and the second predetermined value B to the sensor unit purge rate R _PRGS . Therefore, when the sensor portion purge rate R _PRGS is equal to or less than the purge rate R _PRG , the purge gas concentration estimated value K _{AF_PRG} is _equal to or greater than 0 if at least the predetermined value A is equal to or less than 1. Further, when the sensor purge rate R _PRGS exceeds the purge rate R _PRG , the purge gas concentration estimated value K _{AF_PRG} can be 0 or more by increasing the limit using the second predetermined value B smaller than the predetermined value A. .

The control unit 9 controls the fuel injection amount from the injector 18 and the opening degree of the throttle valve 23 and the purge valve 31. Here, for example, the intake air flow rate Q, the sensor air-fuel ratio AF, the purge rate R _PRG , the sensor part purge rate R _PRGS , the fuel amount correction coefficient K _{FB_PRG} , the purge gas concentration estimated value K _{AF_PRG} , the rotational speed Ne of the engine 10, and the accelerator operation amount A _{Based on PS} , brake fluid pressure _BRK, etc., the respective opening degrees of the throttle valve 23 and the purge valve 31 are controlled. The fuel injection amount is controlled by either feedback injection control or open loop injection control, and is adjusted so that the air-fuel ratio of the air-fuel mixture actually introduced into the cylinder 19 becomes equal to the target air-fuel ratio AF _TGT. .

As described above, in the engine control apparatus 1, the upper limit value K _{MAX of} the fuel amount correction coefficient K _{FB_PRG} corresponding to the sensor portion purge rate R _PRGS is set, and it is avoided that the purge gas concentration estimated value K _{AF_PRG} becomes negative. Thereby, the calculation accuracy related to the estimation of the purge gas concentration estimated value _{KAF_PRG} is improved. In addition, since the fuel injection amount from the injector 18 and the opening degree of the throttle valve 23 and the purge valve 31 are controlled using the purge gas concentration estimated value K _{AF_PRG} with high calculation accuracy, any of feedback injection control and open loop injection control In this case, the calculation accuracy of the fuel injection amount is improved and the controllability is improved.

[3. flowchart]
FIG. 4 is a flowchart illustrating an example of a calculation method of the purge gas concentration estimated value K _{AF_PRG in} the engine control apparatus 1. This flow is repeatedly performed at a predetermined cycle (for example, several tens [ms] cycles) set in advance.

In step A10, the target air-fuel ratio setting unit 3 sets the target air-fuel ratio AF _TGT . Here, for example, the target air-fuel ratio AF _TGT having a magnitude corresponding to the load required for the engine 10 is given. In the next step A20, the exhaust air / fuel ratio information detected by the air / fuel ratio sensor 32 is input to the air / fuel ratio calculating section 4 of the engine control device 1, and the air / fuel ratio calculating section 4 calculates the sensor air / fuel ratio AF. In step A30, information on the intake air flow rate Q detected by the air flow sensor 33 is input to the charging efficiency calculation unit 2, and the charging efficiency Ec is calculated.

In step A40, information such as the opening degree S ₁ of the throttle valve 23, the opening degree S ₂ of the purge valve 31 and the respective flow rates are input to the purge rate calculation unit 5, and the purge rate R _PRG is calculated based on these information. Is done. For example, a value obtained by multiplying the ratio of the opening S ₂ of the purge valve 31 to the opening S ₁ of the throttle valve 23 by a correction coefficient is calculated as the purge rate R _PRG . In this case, the correction coefficient may be set in consideration of the pressure loss of the air passing through the canister 29, or according to the pressure difference of the throttle valve 23 part and the pressure ratio (for example, the ratio of the downstream pressure to the upstream pressure). A magnitude correction coefficient may be set.

In step A50, the sensor portion purge rate R _PRGS is calculated based on the charging efficiency Ec calculated in step A30 and the purge rate R _PRG calculated in step A40. Here, for example, a filter coefficient having a magnitude corresponding to the filling efficiency Ec is set, and first-order lag processing and second-order lag processing using the filter coefficient are performed on the purge rate R _PRG to purge the sensor unit. The rate R _PRGS is required. The filter coefficient is set to such a value that the delay time of the sensor portion purge rate R _PRGS with respect to the purge rate R _PRG becomes shorter as the filling efficiency Ec is higher.

In Step A60, it is determined whether or not the sensor portion purge rate R _PRGS is increasing. In this step, the sign of the change gradient of the sensor unit purge rate R _PRGS is determined. For example, when the sensor unit purge rate R _PRGS calculated in step A50 of the current calculation cycle is compared with the sensor unit purge rate R _PRGS obtained in the previous calculation cycle, the current value exceeds the previous value. Then, it is determined that the sensor purge rate R _PRGS is increasing (the change gradient is positive). On the other hand, when the current value is less than or equal to the previous value, it is determined that the sensor portion purge rate R _PRGS is decreasing (change gradient is negative) or constant (change gradient is 0). Here, if the change gradient is positive, the control proceeds to step A70, and otherwise the process proceeds to step A80.

In step A70, the upper limit value limiting unit 7 sets a value obtained by adding the predetermined value A to the sensor unit purge rate R _PRGS as the upper limit value _KMAX . For example, when the sensor portion purge rate R _PRGS is 0.06 (6%) and the predetermined value A is 1.00, the upper limit value K _MAX is set to 1.06. On the other hand, in step A80, a value obtained by adding the second predetermined value B to the sensor portion purge rate _RPRGS is set as the upper limit value _KMAX . The second predetermined value B is a value smaller than the predetermined value A. For example, when the sensor portion purge rate R _PRGS is 0.06 (6%) and the second predetermined value B is 0.97, the upper limit value K _MAX is set to 1.03. The upper limit value K _MAX set in step A80 acts to limit the value of the fuel amount correction coefficient K _{FB_PRG} more strongly in the decreasing direction than the upper limit value K _MAX set in step A70.

In step A90, the fuel amount correction coefficient calculating unit 6 calculates a fuel amount correction coefficient K _{FB_PRG} based on the sensor air-fuel ratio AF calculated in step A20 and the target air-fuel ratio AF _TGT set in step A10. The fuel amount correction coefficient K _{FB_PRG} calculated in this step is not yet limited. In subsequent step A100, it is determined whether or not the fuel amount correction coefficient K _{FB_PRG} calculated in step A90 is equal to or less than the upper limit value K _MAX set in one of steps A70 and A80.

Here, if K _{FB_PRG} > K _MAX, it is determined that the fuel amount correction coefficient K _{FB_PRG} calculated in step A90 is excessive, and the process proceeds to step A110 where the value of the upper limit value K _MAX is a new fuel amount. The correction coefficient K _{FB_PRG} is set and the process proceeds to step A120. On the other hand, if K _{FB_PRG} ≦ K _MAX , the process directly proceeds to step A120. In this case, the value of the fuel amount correction coefficient K _{FB_PRG} calculated in step A90 is held as it is.

In Step A120, the purge concentration calculation unit 8 calculates the purge gas concentration estimated value K _{AF_PRG} based on the fuel amount correction coefficient K _{FB_PRG} , the sensor unit purge rate R _PRGS and the target air-fuel ratio AF _TGT , and the calculated value is updated to the latest value. It is updated and the control in this calculation cycle is completed. The purge gas concentration estimated value K _{AF_PRG} calculated here is used in the control unit 9 to calculate the fuel injection amount and the opening degree of the throttle valve 23 and the purge valve 31.

When the sensor portion purge rate R _PRGS is 0.06 (6%) and the predetermined value A is 1.00, if the sensor portion purge rate R _PRGS is increasing, the upper limit value K _MAX is 1.06 in step A70 described above. It is said. Thereafter, if the fuel amount correction coefficient K _{FB_PRG} calculated in step A90 is larger than 1.06, the purge gas concentration estimated value K _{AF_PRG} becomes a negative value. However, in the above control, the value of the fuel amount correction coefficient K _{FB_PRG} is limited so as not to exceed the upper limit value K _MAX of 1.06. Therefore, the purge gas concentration estimated value K _{AF_PRG} calculated in step A120 is a value of 0 or more.

[4. Action]
The change of the fuel amount correction coefficient K _{FB_PRG} between the calculation periods by the above control method will be described with reference to FIGS.
When the sensor portion purge rate R _PRGS is increased, a value obtained by adding the predetermined value A to the sensor portion purge rate R _PRGS is set as the upper limit value K _MAX . Here, as shown in FIG. 5A, attention is paid to a period from time t ₁ to time t _{2 in} which the change gradient of the sensor portion purge rate R _PRGS is constant (positive value). Calculation period is 1/4 of the period from time t ₁ to time t _2, when the start time of the operation is a time t _1, the calculation of the fuel amount correction coefficient K _{FB - PRG} from the time t ₁ to time t ₂ Will be implemented five times during Therefore, the value of the fuel amount correction coefficient K _{FB_PRG} is calculated intermittently as indicated by black dots in FIG.

A value obtained by adding the predetermined value A to the sensor unit purge rate R ₁ at time t _1, plotting the value obtained by adding the predetermined value A to the sensor unit purge rate R ₂ at time t ₂ in FIG. 5 (b) These are connected by a broken line graph. This broken line graph has a shape corresponding to the graph of the sensor portion purge rate R _PRGS indicated by the solid line in FIG. 5A, and coincides with that showing the change in the theoretical upper limit value K _MAX . When the five fuel amount correction coefficients K _{FB_PRG} are limited by the upper limit value K _MAX , these five black spots are all located on the broken line.

The value of the fuel amount correction coefficient K _{FB_PRG} obtained in each calculation cycle is held until a new value is obtained in the next calculation cycle. Therefore, for example, in the section from time t ₁ to time t _{11 in} FIG. _5B , the value R ₁ + A of the fuel amount correction coefficient K _{FB_PRG} obtained at time t ₁ is held, and this value R ₁ + Various controls are performed with A as the fuel amount correction coefficient K _{FB_PRG} . Within this interval, R ₁ + A ≦ K _MAX is always _satisfied , and the fuel amount correction coefficient K _{FB_PRG} does not exceed the theoretical upper limit value K _MAX .

On the other hand, if the upper limit value K _MAX is set using the same predetermined value A when the sensor portion purge rate R _PRGS is decreased, the fuel amount correction coefficient K _{FB_PRG} may _{exceed the} theoretical upper limit value K _MAX .
For example, as shown in FIG. 5 (c), the gradient change of the sensor unit purge rate R _PRGS is focused on the period from time t ₃ is constant (negative value) to time t _4. When the fuel amount correction coefficient K _{FB_PRG} calculated during this period is all limited by the upper limit value K _MAX , the calculated value of the fuel amount correction coefficient K _{FB_PRG} indicated by a black dot in FIG. Located on the graph of the theoretical upper limit K _MAX shown.

Meanwhile, since the graph of the upper limit value K _MAX theoretical by a reduction of the sensor unit purge rate R _PRGS is shaped downward, the upper limit value K _MAX is the fuel amount correction coefficient K to be held until the next operation cycle of the theoretical It will fall below the value of _{FB_PRG} . A range indicated by hatching in FIG. 5D indicates a time during which the fuel amount correction coefficient K _{FB_PRG} can exceed the theoretical upper limit value K _MAX and the excess amount.

Based on the relationship between the fuel amount correction coefficient K _{FB_PRG} and the theoretical upper limit value K _MAX , the above control method uses the second predetermined value B when the sensor portion purge rate R _PRGS is decreased, and the upper limit value K. _MAX is set. The second predetermined value B is a value smaller than the predetermined value A, that is, functions to more strongly limit the fuel amount correction coefficient K _{FB_PRG} . Therefore, as shown by a solid line in FIG. 5 (e), the even during the period from the fuel amount correction coefficient K _{FB - PRG} is computed until a new value is obtained in the next calculation cycle, the fuel amount correction coefficient K _{FB - PRG} It is possible not to exceed the theoretical upper limit K _MAX .

[5. effect]
Thus, according to the engine control apparatus 1 of this embodiment, the following operations and effects can be obtained.

(1) In the engine control apparatus 1 described above, the upper limit value K _{MAX of the} fuel amount correction coefficient K _{FB_PRG} is set based on the purge rate R _PRG . Accordingly, the range of the purge gas concentration estimated value K _{AF_PRG} can be specified using the relationship between the purge rate R _PRG and the fuel amount correction coefficient K _{FB_PRG} described in Expression 4.

In addition, since the actual purge gas concentration does not become negative, by _specifying the purge gas concentration estimated value K _{AF_PRG in} the range of 0 or more, it is possible to select from any combination of the purge rate R _PRG and the fuel amount correction coefficient K _{FB_PRG.} Inappropriate combinations can be excluded. Thereby, it is possible to reduce a calculation error for each of the purge rate R _PRG and the fuel amount correction coefficient K _{FB_PRG} .

In general, _since the calculation error of the purge rate R _PRG is smaller than the calculation error of the fuel amount correction coefficient K _{FB_PRG,} by _{obtaining the} fuel amount correction coefficient K _{FB_PRG} based on the purge rate R _PRG , the conventional method is used. In comparison, the calculation accuracy of the fuel amount correction coefficient K _{FB_PRG} can be remarkably improved. Therefore, the estimation calculation accuracy of the purge gas concentration can be improved.

(2) In the engine control apparatus 1 described above, the lower the sensor portion purge rate R _PRGS , that is, the lower the purge rate R _PRG , the lower the upper limit value K _{MAX of the} fuel amount correction coefficient K _{FB_PRG} is set. Restrictions are added. Therefore, it can be easily avoided that the purge gas concentration estimated value _{KAF_PRG} is estimated as a negative value _{due to} the calculation error of the fuel amount correction coefficient _{KFB_PRG} .

In the engine control apparatus 1 described above, a value obtained by adding 1 to the sensor portion purge rate R _PRGS expressed as a percentage is set as the upper limit value K _MAX of the fuel amount correction coefficient K _{FB_PRG} at that time. As a result, the value range of the purge gas concentration estimated value _{KAF_PRG} can be reliably set to 0 or more.

(3) Further, in the engine control apparatus 1 described above, the delay time until the purge gas introduced into the intake system reaches the vicinity of the air-fuel ratio sensor 32 is taken into account when calculating the purge rate R _PRG . For example, a first-order lag process or a second-order lag process is performed on the purge rate R _PRG calculated by the purge rate calculation unit 5 to calculate the sensor unit purge rate R _PRGS .

By accurately simulating the state of the purge gas in the vicinity of the air-fuel ratio sensor 32 and setting the upper limit value K _MAX , the degree of influence of the purge gas on the air-fuel ratio sensor 32 can be determined by the fuel amount correction coefficient K _{FB_PRG} . This can be reflected in the calculation, and the calculation error of the fuel amount correction coefficient K _{FB_PRG} can be reduced. Thereby, the calculation accuracy of the purge gas concentration estimated value _{KAF_PRG} can be improved.

(4) In the engine control apparatus 1 described above, when the sensor portion purge rate R _PRGS is obtained from the purge rate R _PRG , the delay time is estimated based on the charging efficiency Ec. For example, in the upper limit limiting unit 7, the delay time of the sensor purge rate R _PRGS with respect to the purge rate R _PRG is reduced as the filling efficiency Ec is increased (the delay time is extended as the charging efficiency Ec is decreased). ), Time constants and filter coefficients are given. Thus, the influence of the purge gas delay more accurately can be reflected in the calculation of the fuel amount correction coefficient K _{FB - PRG,} the calculation error of the fuel amount correction coefficient K _{FB - PRG} can be further reduced.

(5) In the engine control apparatus 1 described above, the upper limit value K _{MAX of the} fuel amount correction coefficient K _{FB_PRG} is set according to the sign of the change gradient of the sensor portion purge rate R _PRGS . For example, as shown in FIG. 5A, when the change gradient of the sensor portion purge rate R _PRGS is positive, a value obtained by adding a predetermined value A to the sensor portion purge rate R _PRGS is set as the upper limit value K _MAX .

On the other hand, as shown in FIG. 5C, when the change gradient of the sensor portion purge rate R _PRGS is negative or 0, a value obtained by adding the second predetermined value B to the sensor portion purge rate R _PRGS is set as the upper limit value K _MAX. Set and more restrictive than when the slope of change is positive. By setting the upper limit value K _{MAX in} this way, it is possible to avoid a situation in which the value of the fuel amount correction coefficient K _{FB_PRG} temporarily exceeds the upper limit value K _MAX during the calculation cycle.

[6. Modified example]
In the embodiment described above has exemplified what sets the upper limit value K _MAX of the fuel amount correction coefficient K _{FB - PRG} based on the sensor unit purge rate R _PRGS, using purge rate R _PRG instead of the sensor unit purge rate R _PRGS The upper limit value K _MAX may be set. By setting the upper limit value K _MAX of the fuel amount correction coefficient K _{FB_PRG} using at least a parameter corresponding to the purge gas introduction ratio, the range of the purge gas concentration estimated value K _{AF_PRG} can be specified. Incidentally, in order to improve the calculation accuracy of the purge gas concentration estimated value K _{AF - PRG,} it is preferable to set the upper limit value K _MAX using a sensor unit purge rate R _PRGS than purge rate R _PRG.

In the embodiment described above, depending on the sign of the change gradient of the sensor unit purge rate R _PRGS, varies upper limit value K _MAX of calculation method is set, sets the upper limit value K _MAX in a single calculation method It is good also as a calculation structure to perform. That is, the upper limit value K _MAX may be obtained by adding the predetermined value A to the sensor unit purge rate R _PRGS regardless of the sign of the change gradient. For example, if the calculation cycle is short enough that the difference between the fuel amount correction coefficient K _{FB_PRG} and the theoretical upper limit K _MAX between the calculation cycles is not a problem, the control configuration can be simplified by using a single calculation method. Can be

In the above-described embodiment, the predetermined value A and the second predetermined value B that are added to the sensor unit purge rate R _PRGS when the upper limit value K _MAX is calculated are preset (for example, A = 1.00, B = 0.97) is exemplified, but these values may be changed according to the magnitude of the sensor portion purge rate R _{PRGS and} the magnitude of the change gradient. These predetermined value A and second predetermined value B are directly reflected in the value of the upper limit value K _MAX and correspond to the strength of the restriction given to the fuel amount correction coefficient K _{FB_PRG} .

For example, as the predetermined value A is decreased, the upper limit value K _MAX is decreased, and the fuel amount correction coefficient K _{FB_PRG} is also limited to a smaller value. That is, the predetermined value A also affects the strength of feedback injection control. Therefore, even if the predetermined value A and the second predetermined value B are set according to the operating state in consideration of the balance between the calculation accuracy of the purge gas concentration estimated value K _{AF_PRG} required for the engine 10 and the strength of the feedback injection control. Good.

Further, in the above-described embodiment, the example in which the purge gas delay time is calculated using the charging efficiency Ec, which is a parameter equivalent to the air amount, is exemplified, but instead of the charging efficiency Ec, the in-cylinder air amount (mass, volume) or Volume efficiency or the like may be used. As long as at least a parameter correlated with the amount of air introduced into the cylinder 19 of the engine 10, it can be applied to the same calculation as the charging efficiency Ec.
In addition, the kind of the engine 10 in the above-mentioned embodiment is arbitrary, A gasoline engine, a diesel engine, and another combustion type engine can be used.

DESCRIPTION OF SYMBOLS 1 Engine control apparatus 2 Filling efficiency calculating part (air amount calculating means)
3 Target air-fuel ratio setting unit (target setting means)
4 Air-fuel ratio calculation unit (air-fuel ratio calculation means)
5 Purge rate calculation unit (Purge rate calculation means)
6 Fuel amount correction coefficient calculation unit (correction coefficient calculation means)
7 Upper limit limit part (limitation means)
8 Purge concentration calculator (Purge concentration calculator)
9 Control unit 10 Engine 23 Throttle valve 31 Purge valve 32 Air-fuel ratio sensor 33 Air flow sensor
AF _TGT target air-fuel ratio
AF sensor air-fuel ratio (actual air-fuel ratio)
Ec Filling efficiency (air volume)
R _PRG purge rate
R _PRGS sensor purge rate
K _{AF_PRG} purge gas concentration estimate
K _{FB_PRG} Fuel amount correction factor

Claims (4)

In an engine control device for introducing purge gas containing evaporated fuel from a fuel tank into an intake system,
A purge rate calculating means for calculating a purge rate corresponding to the introduction ratio of the purge gas;
Correction coefficient calculating means for calculating a fuel amount correction coefficient for setting the actual air-fuel ratio of the engine to the target air-fuel ratio;
A purge concentration calculating means for calculating the concentration of the purge gas based on the fuel amount correction coefficient calculated by the correction coefficient calculating means and the purge rate calculated by the purge rate calculating means;
Limiting means for setting an upper limit value of the fuel amount correction coefficient calculated by the correction coefficient calculation means based on the purge rate calculated by the purge rate calculation means ;
The engine control apparatus according to claim 1, wherein the limiting means lowers the upper limit value as the purge rate is lower . Air-fuel ratio calculating means for calculating the actual air-fuel ratio based on detection information of a sensor provided in the exhaust system of the engine;
The purge rate calculating means calculates, as the purge rate, a sensor unit purge rate that is an introduction rate considering a delay time until the purge gas introduced into the intake system reaches the sensor,
It said limiting means, based on the sensor unit purge rate, and sets the upper limit value of the fuel amount correction coefficient, the control device according to claim 1, wherein the engine. Air amount calculating means for calculating the amount of air introduced into the cylinder of the engine,
3. The engine control device according to claim 2 , wherein the purge rate calculating means estimates the delay time based on the air amount calculated by the air amount calculating means. It said limiting means, and changing the upper limit value depending on the sign or magnitude of the change gradient of the purge rate, an engine control apparatus according to any one of claims 1-3.

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